refactor: move document transcription, annotation, viewer sub-packages

- transcription/: TranscriptionBlock, Column, EditView, PanelHeader, ReadView,
  Section + transcriptionMarkers, blockConflictMerge, saveBlockWithConflictRetry
  + useBlockAutoSave, useBlockDragDrop hooks
- annotation/: AnnotationLayer, AnnotationShape, AnnotationEditOverlay
- viewer/: PdfViewer, PdfControls + useFileLoader, usePdfRenderer hooks

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/document/transcription/TranscriptionBlock.test-host.svelte

@@ -0,0 +1,48 @@
+<script lang="ts">
+import { provideConfirmService, type ConfirmService } from '$lib/services/confirm.svelte.js';
+import TranscriptionBlock from './TranscriptionBlock.svelte';
+import type { PersonMention } from '$lib/types';
+
+type BlockProps = {
+	blockId: string;
+	documentId: string;
+	blockNumber: number;
+	text: string;
+	mentionedPersons?: PersonMention[];
+	label: string | null;
+	active: boolean;
+	saveState: 'idle' | 'saving' | 'saved' | 'fading' | 'error';
+	canComment: boolean;
+	currentUserId: string | null;
+	onTextChange: (text: string, mentionedPersons: PersonMention[]) => void;
+	onFocus: () => void;
+	onDeleteClick: () => void;
+	onRetry: () => void;
+	onReviewToggle?: () => void;
+	onMoveUp?: () => void;
+	onMoveDown?: () => void;
+	isFirst?: boolean;
+	isLast?: boolean;
+};
+
+let {
+	onServiceReady,
+	mentionedPersons = [],
+	reviewed = false,
+	onReviewToggle = () => {},
+	...blockProps
+}: BlockProps & {
+	onServiceReady: (s: ConfirmService) => void;
+	reviewed?: boolean;
+} = $props();
+
+const service = provideConfirmService();
+onServiceReady(service);
+</script>
+
+<TranscriptionBlock
+	{...blockProps}
+	mentionedPersons={mentionedPersons}
+	reviewed={reviewed}
+	onReviewToggle={onReviewToggle}
+/>